By Leo Notenboom
If I empty the contents of a file and then save it, is the data really deleted?
You’ve recently spent some time on deleting files. I understand that just hitting Shift+Delete doesn’t rid the hard disk of the file, but I’ve long wondered about some other things: Suppose I have an Excel or Word file that contains personal info (say a list of passwords or other sensitive information) and I decide that’s not such a good idea. If I delete all of the information, then save the file, is that information gone forever? Likewise, suppose this file is called “password.xls,” and I create a new (even blank) spreadsheet, save it as the same file (password.xls), and click ‘Yes’ to “Replace existing file?” Have I successfully hidden those passwords (or whatever) forever? Are they off my disk now? Any chance that life could be this simple?
Let me put it this way: when it comes to computers, life is rarely simple.
This situation is no exception.
The short answer to your question is of course not – the data might still be recoverable.
The longer answer is all about why.
Overwritten files aren’t overwritten
The assumption in your question is that when you update a file with new data, or even removing everything within the file, the new file will be written into the exact same place on the hard disk as the original.
That’s a bad assumption. In fact, it’s not really even what you want the programs to do.
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This post is excerpted with Leo’s permission from his blog.
About Leo Notenboom
Leo A. Notenboom is the owner of Puget Sound Software, LLC and the Leo in Ask Leo!. Leo has been in the personal computer and software industry since 1979, as a software engineer, a manager of software engineers, and as a consultant. In 1983 Leo joined what was then a medium sized local company called Microsoft and spent the next 18 years in a wide variety of groups working on a wide variety of software. If you're running Microsoft Windows, if you've used a Microsoft development tool or Microsoft Money, or if you've ever purchased a ticket through Expedia, there's a good chance you've been touched by some of his work. And of course, since 2003, Leo has been answering your tech questions on Ask Leo!